Lubricant comprising a sulfurized mineral oil and a polyvalent metal dithiocarbamate



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Tex., assignors to Texaco Inc., a corporation of Delaware No Drawing.Filed Dec. 18, 1956, Ser. No. 628,980

9 Claims. (Cl. 252-316) This invention relates to improved lubricatingcompositions comprising a sulfurized mineral lubricating oil, and moreparticularly to extreme pressure lubricants of the lead-sulfur type,containing polyvalent metal dithiocarbamates.

Major users of industrial gear lubricants have adopted more severespecification requirements during the past few years, calling amongother things for greatly improved resistance to thickening at elevatedtemperatures in the presence of air in long time tests. This requirementhas been ditficult to meet in otherwise very superior gear lubricants,particularly in the heavier grades of the better gear lubricants,wherein parafiinic residual oils are employed in order to obtain thedesired viscosity characteristics and other advantages.

in accordance with this invention, very superior extreme pressurelubricants having the combination of properties required to meet themore severe requirements are obtained by employing as the base oil astably sulfurized lubricating oil and in combination therein a minor butsubstantial amount of a lead soap, a minor amount of a sulfurized fattyoil and a minor amount of a polyvalent metal dithiocarbamate. We havefound that a combination of superior properties is obtained in thesecompositions which is not obtainable in other lead-sulfur gearlubricants of the prior art. They have a considerable advantage overlead-sulfur gear lubricants of the usual type in that they contain onlya very small amount of sulfur in the active form, and they thereby avoidthe sludging and other difficulties associated with high contents ofloosely bound, reactive sulfur. In addition, they provide the desiredcombination of high load bearing properties, represented by OK Timkenvalues of at least about 45, and the very superior resistance tothickening required to give a 15 percent maximum viscosity increase bythe extreme pressure oil oxidation by bubbling dry air method,hereinafter referred to as the extreme pressure oil oxidation test,specified in the United States Steel Lubricants Testing Laboratory No.220 Lubricant Performance Requirements for Extreme Pressure Oil.

The stably sulfurized lubricating oils employed in these compositionsare obtained by heating mineral lubricating oils with sulfur for a longtime until the sulfurized products are substantially non-corrosive tometals. In this reaction, upon the prolonged heating, the reactivesulfur groups which are formed in the first stage of the reactiondisappear and substantial thickening of the oil The product is thereforea material of very different character from the corrosive sulfurizedoils ordinarily employed in lubricant compositions of this type whichare obtained by heating the oils with sulfur for a short time only. Thestably sulfurized mineral lubricating oil may be obtained by heating asuitable mineral lubricating oil with about 1 to 5 percent of sulfur ata temperature above about 350 F. and preferably at about 400 F. to 500F. for several hours, so as to obtain a reaction product which issubstantially non-corrosive to copper in the copper strip corrosion testat 212 F. The quantity of sulfur employed is calculated to give about0.3 to about 1.5 percent, and preferably from about 0.5 to 1.2 percent,of sulfur in the oil. The lubricating oils employed in the sulfurizationmay be distillate or rates Patent 0 Patented Sept. 12, 1961 ice Thesulfurized fatty oil may be any of the sulfurized natural orsynthetically obtained fatty materials which have been employedheretofore as lubricant additives of the active sulfur type, such as maybe obtained, for

example, by sulfurizing lard oil, sperm oil, corn oil, or the like. Aparticularly suitable material of this character is sulfurized lard oilcontaining from about 5 to 12 percent of the sulfur, obtained by heatinglard oil with about 10 to 15 percent of sulfur at a temperature about300 F. and preferably at about 350-400 F., for

a suificient time to obtain a homogeneous product.

About 0.5 to 5 percent, and preferably about 1 to 3 percent, by weightof this sulfurized oil may be employed in the lubricating composition.

The polyvalent metal dithiocarbamates employed are salts of organicsubstituted dithiocarbamic acids as described, for example, in U.S.2,400,106. They are preferably polyvalent metal salts of N-aliphatichydrocarbon substituted dithiocarbamic acids containing sufiicientaliphatic carbon atoms to impart oil solubility to the molecule, andmost advantageously those wherein each nitrogen is substituted byaliphatic hydrocarbon groups containing about 4 to 20 carbon atoms.Suitable polyvalent metals include, for example, the alkaline earthmetals, zinc, cadmium, magnesium, tin, aluminum and iron. Metals of thegroup II subgroup consisting of magnesium, cadmium and zinc areespecially suitable. As examples of this preferred group of compoundsmay be mentioned zinc dibutyl dithiocarbamate, zinc diamyldithiocarbamate, zinc di(2-ethylhexyl) dithiocarbamate, cadmium dibutyldithiocarbamate, cadmium dioctyl dithiocarbamate, cadmium octyl-butyldithiocarbamate, magnesium dibutyl dithiocarbamate, magnesium dioctyldithiocarbamate, zinc petroleum base dithiocarbamates. and cadmiumdicetyl dithiocarbamate. Especially desirable compounds of this classare zinc dibutyl dithiocarbamate, zinc diamyl dithiocarbamate, andcadmium dibutyl dithiocarbamate, which are commercially availablematerials. The polyvalent metal dithiocarbamate is usually employed inamounts of about 0.2-5 percent by weight, although somewhat larger orsmaller amounts may be employed if desired, such as from about 0.1 toabout 10 percent by weight.

The high stability against oxidative thickening in the extreme pressureoil oxidation test obtained in these compositions is surprising, sincecompositions comprising these stably sulfurized mineral oils have notbeen inhibited in this test by numerous other oxidation inhibitors ofvarious types, including some of the most generally effective oxidationinhibitors commonly employed in lubricating compositions. In addition,the dithiocarbamates are of generally inferior oxidation inhibitingeffectiveness in mineral lubricating oils of the ordinary types in theusual tests. The following table shows, for example, the effect of zincdibutyl dithiocarbamate in an unsulfurized mineral lubricating oil inthe Penn State oxidation test, as compared with the efiect of a commonoxidation inhibitor of a different type. The Penn State oxidation testis a well-known test employed for determining the oxidation resistanceoflubricating compositions, and is carried out by circulating oxygen ina closed system thrpugh a 2.50

gram sample of the test oil in a glass tube at a rate of liters per hourfor 40 hours while the oil is maintained at 338 F. The lubricating oilemployed was a refined paralfinic distillate oil having a viscosity of3-28 seconds SU at 100 F. (kinematic viscosity of 71.0). The table alsoshows the strong pro-oxidant effect of. lead naphthenate upon. the samemineral lubricating oil in this test.

As shown by the above table, the unsulfurized mineral luubricating oilcontaining zinc dibutyl dithiocarbamate had thickened only slightly lessthan the base oil alone after 40 hours at 338 F. The compositioncontaining zinc dibutyl dithiocarbamate had a characteristic highinitial oxidation resistance in this test, an oxygen absorption curve ofthe test showing -a long induction period of about 18 hours, followed bya very rapid increase in oxygen absorption so that at the end of the 40hour period the oxygen absorption had almost equaled that of theuninhibited oil.

In contrast with the failure of the polyvalent metal dithiocarbamates toinhibit other types of mineral lubri cating oils over long periods oftime, as shown by the above test, the compounds of this class areextremely eflective in inhibiting the stably sulfurized minerallubrieating oils employed in the lubricating compositions of thisinvention even in the presence of. strong pro-oxidants such as, leadnaphthenate.

Thefollowing examples are given for the purpose of further disclosingthe invention.

Example I A gear lubricant representative of a preferred embodiment ofthis invention was preparedv comprising a sulifurized minerallubricating oil containing 7.5 percent of lead naphthenate, 2.0 percentof sulfurized lard oil and zinc dibutyl dithiocarbamate in amounts ofboth 0.5 and 1. percent by weight. The composition also contained 50parts per million of an antifoam compound, which. was a 1.0 percent byweight solution of a dimethyl silicone polymer in kerosene.

The sulfurized mineral oil employed was a blend of sulfurized heavyparafinic residual oil and a sulfurized light. paraffinic distillateoil. The sulfurized. heavy residua'l oil was obtained by heating aresidual oil having a viscosity of 381 seconds Saybolt Universal at 21.0F. forabout 4.5 hours at 440 F. with 2.0 percent sulfur; and finallysteaming in a vacuum tower to remove hydrogen sulfide. The product. hada viscosity of 457 seconds Saybolt Universal at 210 F. and contained0.92 percent sulfur. The light parafiinic distillate oil was a fractionhaving a viscosity of about 168 seconds Saybolt Universal at 100 F., andwas sulfurized. in the form of a 476 seconds viscosity blend with aminor portion of the heavy residual oil described. above by heating theblend for about 8 hours at 445 F. with 2.8 percent sulfur, and. finallysteaming in. a vacuum tower to remove hydrogen. sulfide. The product hada viscosity of 591 seconds Saybolt Universal at 100 F. and contained0.73 percent sulfur. Both oils were substantially non-corrosive tocopper in the copper strip corrosion test at. 212 F. The. sulfurizedstocks were: each mixed with 2.16 percent by weight. of sulfurized lardoil, based on the weight of the blend,. and; then; blended. together inaboutv a 31.5:55 byweight ratio of heavy to'light oil.

The sulfurizedlard oilemployed was obtained by heat. ing a No. I lardoil at about 300 F. for 4 hours while powdereds'ulfur. was added in aproportion of 33 pounds of powdered sulfur per barrel to 170 barrels oflard oil, then heating for 8 hours longer at 300-405 F. and finallysteaming in a vacuum tower to remove hydrogen sulfide. The productcontained 7.09 percent of sulfur and had a viscosity of 217 secondsSaybolt Universal at 210 F.

The zinc dibutyl dithiocarbamate employed was commercial product sold bythe R. T. Vanderbilt Company under the name Butyl Zimate. Typical testson this material show a melting point of 106 C., a sulfur content of28.25 percent. and zinc content of 14.3 percent.

The lubricant was prepared by mixing the above mate rials in theproportions indicated in an ordinary grease kettle for about 3 hourswhile the temperature was maintained at about 160200 F., and drawing atabout F.

The following table shows the results obtained upon this lubricant inthe extreme pressure oil oxidation test, together with comparative dataupon the same composition without the zinc dibutyl dithiocarbamate andalso upon the composition containing various other inhibitors ofdiiferent types in place of the zinc dithiocarbamate. This test iscarried out by circulating 10 liters of dry air continuously through a300 ml. sample of the test oil in a: glass tube fora period of 13 days(312 hours) while the temperature of the test oil is maintained at about200 F 207 F. The viscosity of the oil, at 210 F. is determinedboth-beforeand after the test.

TABLE II Viscosity Goncenincrease, Inhibitor tration SUS at percent 210F percent Nona. r 18. 6 Phenyl-alpha-naphthylamine; 0. 5 21. 4 N,N,N,Ntetramethyldiamino diphenylmethane 0. 5 22. ON,Ndisalicylidene-l,Z-diaminopropene 0. 5 17. 5 2,6-ditertiarybutyl-4-methyl phenol 0. 5 18. 6 Diphenylamine 0. 5 21. 9 0. 5 21. 6 0.5 21. 0 Ditertiary butyl-paracresol 0. 5 17. 4 Vanlube 26 1 1. 0 17. lCalco 2246 1. 0 30. 3 Zinc dibutyl dlthiocarbama 0. 5 11.7 Zinc dibutyldithiocarbamate- 1. 0 6. 6

1 Commercial oxidation inhibitors otnnlmown composition.

As shown by the above table, thickening of the composition comprisingthe stably sulfurized mineral lubricating oil was inhibited to wellbelow the required 15 percent maximum in the extreme pressure oiloxidation test by means of 0.5 percent of the polyvalent metaldithiocarbamate, and a still further inhibiting efiect was obtained byincreasing the amount of polyvalent metal dithiocarbamate to 1.0percent. In very striking contrast to the inhibiting effectivenessobtained by means of this compound, the other compounds of various typeswhich are commonly employed as antioxidants in lubricating compositionswere almost entirely ineffective or even increased the amount ofthickening in this test.

In addition to the high stability against oxidative thickening as shownby the above table, this composition had high load bearing propertiesand other advantages, as shown by the following inspection testsobtained upon the composition containing 1.0 percent of zinc dibutyldithiocarbamate:

Viscosity, SUS, at 210 F 125.7

Example II TABLE III Zinc dibutyl Viscosity dithiocarbaincrease, SUS,mate, percent at 210 F., by weight percent As shown by the above table,the composition based on the sulfurized paraffinic residual oil alonewas also inhibited to the required degree by employing higherproportions of the polyvalent metal dithiocarbamate.

While the combination of stably sulfurized mineral lubricating oil andpolyvalent metal dithiocarbamate is employed with particular advantagein the production of superior gear lubricants of the lead-sulfur type asdescribed above, the use of this combination of stably sulfurizedmineral lubricating oil and polyvalent metal dithiocarbamate in otherlubricating compositions is also contemplated, and it may be employedeither alone or together with other additives of various types whereversuperior resistance to oxidation and other special properties aredesired. Other extreme pressure agents which may be employed in thesecompositions include particularly phosphorus acid esters, such astricresyl phosphate, other heavy metal soaps, and other active sulfurcompounds, such as dibenzyl disulfide, diphenol disulfide, dioctylsulfide, dicyclohexyl disulfide, sulfurized cyclohexene, sulfurizedterpinolene, sulfurized oleyl alcohol, etc. Additives of other types,including other oxidation inhibitors, particularly those of the aminetype, such as diphenylamine, diphenyl-para-phenylene diamine, etc.,corrosion inhibitors, anti-foam agents, etc., may also be employed.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made Without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. A lubricating composition consisting essentially of a stablysulfurized mineral lubricating oil in major proportion containing about0.3 to 1.5 percent by weight of combined stable sulfur, about 5-20percent by weight of a lead soap selected from the group consisting oflead naphthenates and lead soaps of fatty acids containing at least 8carbon atoms per molecule, about 0.55 percent by weight of a sulfurizedfatty oil, and about 0.1 to 10 percent by weight of an oil solublepolyvalent metal dithiocarbamate, wherein the said polyvalent metal ischosen from the group consisting of alkaline earth metals, cadmium andzinc, said stably sulfurized mineral lubricating oil being obtained byheating a mineral lubricating oil with sulfur at a temperature aboveabout 350 F. until a sulfurized product is obtained wherein the sulfuris present substantially entirely in a form which is nonreactive withcopper in the copper strip corrosion test at 212 F.

2. The lubricating composition of claim 1 wherein the said oil-solublepolyvalent metal dithiocarbamate is chosen from the group consisting ofmagnesium, cadmium, and zinc salts of N-aliphatic hydrocarbonsubstituted dithiocarbamate acids containing from about 8 to 40aliphatic carbon atoms.

3. A lubricating composition consisting essentially of a stablysulfurized mineral lubricating oil in major proportion containing about0.5 to 1.5 percent by weight of combined stable sulfur, about 0.5 to 5percent by weight of an oil-soluble zinc dithiocarbamate, about 5-20percent by weight of a lead soap selected from the group consisting oflead naphthenates and lead soaps of fatty acids containing at least 8carbon atoms per molecule and about 0.5 to 5 percent by weight of asulfurized fatty oil, said stably sul-furized mineral lubricating oilbeing obtained by heating a mineral lubricating oil with sulfur at atemperature above about 350 F. until a sulfuri'zed product is obtainedwherein the sulfur is present substantially entirely in a form which isnonreactive with copper in the copper strip corrosion test at 212 F.

4. The lubricating composition of claim 3 wherein the said lead soap islead naphthenate.

5. The lubricating composition of claim 3 wherein the said sulfurizedfatty oil is sulfurized lard oil containing about 5-12 percent by weightof sulfur.

6. A lubricating composition consisting essentially of a stablysulfurized mineral lubricating oil containing about 0.5 to 1.5 percentof combined stable sulfur, about 0.5 to 5 percent by weight of an oilsoluble Zinc dialkyl dithiocarbamate wherein the said alkyl groups eachcontains from about 4 to 20 carbon atoms, about 7 to 15 percent byweight of lead naphthenate and about 1 to 3 percent by weight ofsulfurized lard oil containing about 5 to 12 percent of sulfur, saidstably sulfurized mineral lubricating oil being obtained by heating amineral lubricating oil with sulfur at a temperature above about 350 F.until a sulfurized product is obtained wherein the sulfur is presentsubstantially entirely in a form which is nonreactive with copper in thecopper strip corrosion test at 212 F.

7. The lubricating composition of claim 6 wherein the said oil solublezinc dithiocarbamate is zinc dibutyl dithiocarbamate.

8. The lubricating composition of claim 6 wherein the said stablysulfurized mineral lubricating oil is a sulfurized parafiinic oil.

9. The lubricating composition of claim 6 wherein the said stablysulfurized mineral lubricating oil comprises at least about 50 percentby weight of a sulfurized paraffinie residual oil.

References Cited in the file of this patent UNITED STATES PATENTS2,142,916 Parkhurst Jan. 3, 1939 2,212,189 Brunstrum Aug. 20, 19402,246,282 Zimmer et al. June 17, 1941 2,265,851 Matheson Dec. 9, 19412,400,106 Denison et al May 14, 1946 2,629,694 Woods et a1 Feb. 22, 19532,813,076 Edelman et al Nov. 12, 1957 2,820,011 Mahoney et al. Jan. 14,1958 2,836,561 Elliott et al May 27, 1958 OTHER REFERENCES Kalichevskyet al.: Petroleum Refining with Chemicals, Elservier Pub. Go, January1956 (pages 590 and 597).

1. A LUBRICATING COMPOSITION CONSISTING ESSENTIALLY OF A STABLYSULFURIZED MINERAL LUBRICATING OIL IN MAJOR PROPORTION CONTAINING ABOUT0.3 TO 1.5 PERCENT BY WEIGHT OF COMBINED STABLE SULFUR, ABOUT 5-20PERCENT BY WEIGHT OF A LEAD SOAP SELECTED FROM THE GROUP CONSISTING OFLEAD NAPHTHENATES AND LEAD SOAPS OF FATTY ACIDS CONTAINING AT LEAST 8CARBON ATOMS PER MOLECULE, ABOUT 0.5-5 PERCENT BY WEIGHT OF A SULFURIZEDFATTY OIL, AND ABOUT 0.1 TO 10 PERCENT BY WEIGHT OF AN OIL SOLUBLEPOLYVALENT METAL DITHIOCARBAMATE, WHEREIN THE SAID POLYVALENT METAL ISCHOSEN FROM THE GROUP CONSISTING OF ALKALINE EARTH METALS, CADMIUM ANDZINC, SAID STABLY SULFURIZED MINERAL LUBRICATING OIL BEING OBTAINED BYHEATING A MINERAL LUBRICATING OIL WITH SULFUR AT A TEMPERATURE ABOVEABOUT 350*F. UNTIL A SULFURIZED PRODUCT IS OBTAINED WHEREIN THE SULFURIS PRESENT SUBSTANTIALLY ENTIRELY IN A FORM WHICH IS NONREACTIVE WITHCOPPER IN THE COPPER STRIP CORROSION TEST AT 212*F.